Visual System Quiz on Eye Anatomy

Lecture 4: Special Senses

• Lecture covers the special senses focusing on visual, chemical (taste and smell), auditory, and vestibular systems.
• Material references Sherwood Chapter 5.

Objectives

• The visual system is covered.
• Chemical senses (taste and smell) are explored.
• Structure of the auditory system investigated.
• The vestibular system is examined.

The Visual System

• 70% of all sensory receptors are located in the eye.
• The eye is protected by a cushion of fat and the bony orbit.
• Accessory structures include eyebrows, eyelids, eyelashes, and eye muscles.
• Eyebrows shade the eye, prevent perspiration.
• Eyelids protect the eye, contain glands secreting oily secretions.
• Eyelashes initiate reflex blinking.
• Eye muscles control eye movement.

Visual System: Extraocular Muscles

• Lateral Rectus Muscle: abducts the eye.
• Medial Rectus Muscle: adducts the eye.
• Superior Rectus Muscle: moves the eye upward.
• Inferior Rectus Muscle: moves the eye downward.
• Superior Oblique Muscle: moves the eye downward.
• Inferior Oblique Muscle: moves the eye upward.

Visual System: Structures of the Eye

• Cornea: transparent, protective covering of the iris and pupil.
• Sclera: connective tissue layer, the whites of the eye.
• Conjunctiva: epithelial tissue layer connecting sclera to eyelids.
• Lacrimal Glands: secrete aqueous tear film lubricating the eye.
• Iris: the colored part; regulates the amount of light entering the eye.
• Pupil: central opening of the iris, adjusts to light.

Visual System: Internal Structures of the Eye

• Fibrous Layer: sclera and cornea.
• Vascular Layer: choroid, ciliary body, iris
• Sensory Layer: retina.
• Lens: transparent, protein-filled structure supporting focusing.
• Retina: light-sensing tissue at the back of the eyeball, delicate two-layered membrane.

Visual System: Retinal Layers

• Pigmented layer: outer layer, absorbs stray light rays, phagocytic function.
• Neural layer: processes visual data before sending signals via optic nerve.

Visual System: Cells of the Retina

• Photoreceptors: rods (numerous, see in dim light, only grayscale) or cones (less numerous, respond to bright light, produce color vision).
• Ganglion cells: receive visual information from photoreceptors, send information to the optic nerve, ON and OFF responses.
• Bipolar Cells: receive signals from photoreceptors, transmit signals to ganglion cells.
• Horizontal cells: modulate signaling between photoreceptors and bipolar cells, allow for bright/dim light adjustments.
• Amacrine cells: modulate signaling between ganglion and bipolar cells.

Visual System: Cells of the Retina (detailed)

• Outer segment of photoreceptors detects light stimuli.
• Inner segment of photoreceptors is the metabolic area.
• Synaptic terminal transmits signals to bipolar cells.

Visual System: Light Sensitive Photopigment

• Rhodopsin is the light-sensitive photopigment in rods; absorbs all light wavelengths.
• Photopsin is the light-sensitive photopigment in cones; three types (red, green, blue) allowing color vision.

Visual System: Dark Vision (Rods)

• Light absorption causes retinal to change shape, starting the conversion of energy to action potential.
• In the dark: 11-cis-retinal.
• In the light: all-trans-retinal.

Visual System: Color Vision (Cones)

• Three types of photoreceptors (red, green, blue cones).
• Colour vision is the combination of cones stimulating.
• Colour blindness occurs from a lack of one or more cone types.

Visual System: Phototransduction Cascade

• Light triggers a cascade of events, eventually leading to hyperpolarization.
• Hyperpolarization reduces neurotransmitter (glutamate) release, which initiates the visual signal.

Visual System: Optic Tracts

• Action potentials are sent along optic nerve fibers, meeting at the optic chiasm.
• Visual information is sent along optic tracts, crossing over; reaching visual cortex.
• Visual cortex is in the occipital lobe.

Chemical Senses (Taste and Smell)

• Chemical senses include gustation (taste) and olfaction (smell).
• Chemoreceptors respond to chemicals in a solution.
• Taste uses saliva.
• Smell uses fluids of the nasal membranes.

Taste Receptors

• Taste receptors (gustation) are located in small, depressed areas on the tongue called fissures, and are G-protein-coupled receptors.
• Five basic tastes: sweet, sour, salty, bitter, umami.
• Taste is significantly impacted by smell.
• Taste perceived in the brain via the facial (CN VII), and glossopharygeal (CN IX) nerves.
• Tongue map is a myth.

Smell Receptors (Olfaction)

• Smell receptors (olfaction) are located in the olfactory epithelium in the upper part of the nasal cavity.
• Chemical detection occurs in a dissolved fluid in the nose.
• Smell receptors are positioned to detect airborne scents by sniffing.
• Signals are carried via the olfactory nerve to the brain.

The Auditory System

• Hearing (sound) occurs within the inner, middle, and outer ear.
• Outer and middle ear are for hearing.
• Inner ear handles both hearing and equilibrium.
• Hearing receptors are mechanoreceptors (stimulated by physical motion/vibrations).

The Ear

• Ear houses hearing and equilibrium.
• Receptors respond to separate stimuli; independent activation.
• Receptors are mechanoreceptors- reacting based on physical motion.

Anatomy of the Ear

• External ear (pinna and external auditory meatus).
• Middle ear (tympanic membrane, auditory ossicles, auditory tube).
• Internal ear (cochlea, vestibule, semicircular canals).

External Ear

• Pinna (auricle)
• External acoustic meatus: lined with ceruminous glands secreting earwax.
• Tympanic membrane (eardrum): separating external and middle ear.
• Vibrates in response to sound.

Middle Ear

• Includes the tympanic membrane and three auditory ossicles (malleus, incus, stapes).
• Sound vibrations travel from the eardrum to the inner ear.
• Eustachian (auditory) tube connects to the throat for equalizing pressure in the middle ear.
• Otitis media involves middle ear inflammation.

Middle Ear: Structure and Function

• Ossicles are small bones in the middle ear (malleus, incus, stapes).
• Vibrations from the eardrum are transmitted to the inner ear via the ossicles.

Inner Ear

• Made of fluid-filled chambers (bony labyrinth) and suspended membranous labyrinth.
• Cochlea, vestibule, semicircular canals are key structures.
• Contains the spiral organ (Organ of Corti) critical to hearing; hair cells are the receptors.

Inner Ear: Detailed

• Cochlea and hair cells (stereocilia) are sensitive to fluid movement.
• Bending of hair cells generates nerve impulses sent to the auditory cortex.

Sound Transduction

• Sound waves vibrate the eardrum.
• This vibration moves the ossicles, amplifying the sound.
• The ossicles transmit vibrations to the oval window of the inner ear.
• Fluid in inner ear moves affecting the basilar membrane and hair cells
• Bending of hair cells triggers nerve impulses to the auditory cortex.

Auditory Pathway

• The auditory pathway transmits nerve impulses from the inner ear to the auditory cortex.
• Details include various specific relay structures and nuclei.

Deafness

• Sensorineural: impaired hair cells, cochlear nerve, or auditory cortex neurons; often caused by prolonged drug exposure or noise.
• Conduction: occurs when sound vibrations can't reach inner ear (due to eardrum damage or earwax buildup).

The Vestibular System

• Deals with head position and movement.

Vestibular Apparatus

• Semicircular canals: filled with fluid; help detect rotational movements.
• Vestibule: contains otolithic organs (utricle, saccule).
• Detect linear head movements (static equilibrium).

Anatomy of the Vestibular Apparatus

• Bony labyrinth: filled with perilymph.
• Membranous labyrinth: suspended in perilymph, filled with endolymph.

Equilibrium

• Responds to head movement.
• Equilibrium receptors in the inner ear (vestibular apparatus).
• Static equilibrium: vestibule (detect changes in static head position).
• Dynamic equilibrium: semicircular canals (detect rotational head movements)

Static Equilibrium

• Receptors in the vestibule (maculae) that are embedded with otoliths.
• Detect head position relative to gravity.

Dynamic Equilibrium

• Receptors in semicircular canals (cristae ampullaris).
• Detect angular or rotational head movements.

Balance/Equilibrium

• Depends on inputs from the internal ear, vision, and muscle/tendons.
• Receptors in semicircular canals and otolith organs send signals.
• Signals are processed to manage balance.

Balance and Orientation Pathways

• Three modes of input: vestibular, visual, and somatic receptors.
• The signal is sent to the cerebellum.

Input and Output of the Vestibular Nuclei

• Input coming from the eyes, skin, and joints is sent to be processed in the brain.
• Output of the vestibular nuclei travels to motor neurons of limbs, torso, and eyes to maintain balance.

Homeostatic Imbalance: Motion Sickness

• Motion sickness occurs when input from the vestibular apparatus and visual system don't match.
• Disagreements between the body's perceived movement and surroundings lead to motion sickness.

Lecture 4 Pop Quiz Questions and Answers

• (Specific questions and possible answers are not given in the supplied text)

Test your knowledge on the visual system and eye anatomy with this comprehensive quiz. Explore topics such as photoreceptors, neurotransmitter release, and the role of different cells in vision. Perfect for students studying biology or anatomy!